1. Field of the Invention
The present invention relates to a heat pump type air conditioner, and, more particularly, to a heat pump type air conditioner having an improved defrosting structure that is capable of removing frost accumulated on an outdoor heat exchanger while minimizing user discomfort when a heating operation is performed in low-temperature outdoor air. Also, the present invention relates to a defrosting method for such a heat pump type air conditioner.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating the structure of a conventional heat pump type air conditioner. As shown in FIG. 1, the conventional heat pump type air conditioner comprises: a compressor 11 for compressing and circulating refrigerant; a four-way valve 12 for converting the flow direction of the refrigerant such that the refrigerant can flow either in the forward or reverse direction; an outdoor heat exchanger 13 configured to serve as a condenser when a cooling operation is performed and an evaporator when a heating operation is performed; an outdoor fan 14 for suctioning outdoor air; an indoor heat exchanger 15 configured to serve as an evaporator when a cooling operation is performed and a condenser when a heating operation is performed; an indoor fan 16 for suctioning indoor air; and an expansion valve 17 disposed between the outdoor heat exchanger 13 and the indoor heat exchanger 15 for changing the refrigerant into low-temperature and low-pressure gas refrigerant.
The condenser serves to remove heat from high-temperature and high-pressure gas refrigerant such that the high-temperature and high-pressure gas refrigerant is cooled, and therefore, is liquefied. On the other hand, the evaporator serves to lower the temperature of air coming into contact with the surface of the evaporator such that the temperature of moisture in the air falls below the dew point, and therefore, the moisture is changed into water drops, which will be removed.
The four-way valve 12 serves to convert the flow direction of the refrigerant such that the refrigerant discharged from the compressor 11 can flow to the outdoor heat exchanger 13 when a cooling operation is performed and to the indoor heat exchanger 15 when a heating operation is performed.
The operation of the conventional heat pump type air conditioner with the above-stated construction will be described below in detail.
When a user operates the conventional heat pump type air conditioner in cooling mode, the compressor 11 compresses refrigerant, and then supplies the compressed refrigerant to the outdoor heat exchanger 13. The outdoor heat exchanger 13 performs heat exchange between the refrigerant introduced into the outdoor heat exchanger 13 and air suctioned by the outdoor fan 14. As a result, the refrigerant is condensed into room-temperature and high-pressure liquid refrigerant, and the temperature of the air is increased. The increased-temperature air is discharged out of the air conditioner by the outdoor fan 14. The refrigerant condensed by the outdoor heat exchanger 13 passes through a capillary tube, with the result that the condensed refrigerant is changed into low-temperature and low-pressure liquid refrigerant. The indoor heat exchanger 15 performs heat exchange between the refrigerant introduced into the indoor heat exchanger 15 and air suctioned by the indoor fan 16. As a result, the refrigerant is changed into a low-temperature and low-pressure vapor refrigerant, and the temperature of the suctioned air is decreased. The low-temperature and low-pressure vapor refrigerant is delivered to the compressor through refrigerant piping, and the decreased-temperature air is discharged into the interior of a room by the indoor fan 15 to cool the interior of the room.
When the user operates the conventional heat pump type air conditioner in heating mode, on the other hand, the four-way valve 12 converts the flow direction of the refrigerant such that the refrigerant can flow from the compressor 11 to the indoor heat exchanger 15. In this case, the outdoor heat exchanger 13 serves as an evaporator, and the indoor heat exchanger 15 serves as a condenser. As a result, a heating operation is performed.
When the outdoor temperature drops to approximately 5° C. to 6° C. (relative humidity 80%), the surface temperature of the outdoor heat exchanger 13 falls below 0° C., and therefore, moisture in the outdoor air is accumulated on the surface of the outdoor heat exchanger 13. As a result, an air channel created by the outdoor fan 14 is interrupted. Consequently, the thermal efficiency of the outdoor heat exchanger is decreased, and the heating efficiency of the heat pump is significantly decreased.
In order to solve the above-mentioned problems, a defrosting operation for removing front accumulated on the surface of the outdoor heat exchanger 13 is performed. The defrosting operation will be described below in detail with reference to FIG. 2. After a heating operation has been performed for a predetermined period of time, for example, 30 minutes, the temperature of the indoor heat exchanger is measured by an indoor heat exchanger temperature sensor 18 (see FIG. 1), the temperature of the interior of the room is measured by a room temperature sensor 19 (see FIG. 1), and then it is determined whether the outdoor unit is to be defrosted based on the difference between the measured temperature of the indoor heat exchanger and the measured temperature of the interior of the room (Step S1). When it is determined that the outdoor unit is to be defrosted, a pressure balancing operation is performed for approximately 3 minutes, and then a defrosting operation is initiated (Step S2). The defrosting operation is performed for a predetermined period of time, for example, approximately 9 minutes (Step S3). The time required to perform the defrosting operation is set based on the difference between the temperature of the indoor heat exchanger and the temperature of the interior of the room. Subsequently, another pressure balancing operation is performed for approximately 3 minutes, and then a heating operation is performed (Step S4). As can be easily understood from the above description, the pressure balancing operation is performed for approximately 3 minutes, during which time the heating operation is paused. Consequently, it is not possible to perform the heating operation while the defrosting operation is performed. Furthermore, cool air is delivered to the interior of the room from the outdoor heat exchanger, and therefore, the temperature of the interior of the room is lowered, which inconveniences the user. In addition, the outdoor temperature is deduced from the difference between the temperature of the indoor heat exchanger and the temperature of the interior of the room. Consequently, it is difficult to accurately obtain a period of time for which the defrosting operation is performed, and therefore, it is difficult to smoothly perform the defrosting operation.